Total synthesis of emericellamides A and B

Determination of the Absolute Configuration of the Male-Produced Sex Pheromone of the Stink Bug Pellaea stictica, (2R,4R,8R)-2,4,8,13-Tetramethyltetradecan-1-ol by Stereoselective Synthesis Coupled with Enantiomeric Resolution

In a previous study, we reported the identification and synthesis of a male-specific sex pheromone component of the stink bug, Pellaea stictica, as the alcohol 2,4,8,13-tetramethyltetradecan-1-ol (1). To establish the correlation between the stereochemistry of the pheromone and its bioactivity, it first was necessary to determine its absolute configuration. For this purpose, a series of syntheses were designed to: (a) furnish a mixture of all possible stereoisomers; (b) a narrowed down group of diastereomers, and (c) one specific enantiomer. A crucial step in the syntheses involved a coupling reaction between two key intermediates: a phosphonium salt and an aldehyde, through a Wittig olefination. Nuclear magnetic resonance data of a mixture of the synthetic pheromone diastereomers and further comparison of GC retention times with that of the natural product by gas chromatography suggested that the methyl branches at C2 and C4 were in a syn relationship, reducing the possibilities to only four of the eight possible stereoisomers. Employing GC analysis, chiral derivatization reagents and synthetic (8R)-2,4-syn-1 it was possible to confirm the configuration of the methyl branch at C8 as R, reducing the number of possible stereoisomers to two. After enantioselective synthesis of (2R,4R,8R)-1, the absolute configurations of all methyl branches of the natural compound were confirmed as R, fully identifying the male-produced sex pheromone of P. stictica as (2R,4R,8R)-2,4,8,13-tetramethyltetradecan-1-ol.

Marine Cyclic Peptides: Antimicrobial Activity and Synthetic Strategies

Oceans are a rich source of structurally unique bioactive compounds from the perspective of potential therapeutic agents. Marine peptides are a particularly interesting group of secondary metabolites because of their chemistry and wide range of biological activities. Among them, cyclic peptides exhibit a broad spectrum of antimicrobial activities, including against bacteria, protozoa, fungi, and viruses. Moreover, there are several examples of marine cyclic peptides revealing interesting antimicrobial activities against numerous drug-resistant bacteria and fungi, making these compounds a very promising resource in the search for novel antimicrobial agents to revert multidrug-resistance. This review summarizes 174 marine cyclic peptides with antibacterial, antifungal, antiparasitic, or antiviral properties. These natural products were categorized according to their sources—sponges, mollusks, crustaceans, crabs, marine bacteria, and fungi—and chemical structure—cyclic peptides and depsipeptides. The antimicrobial activities, including against drug-resistant microorganisms, unusual structural characteristics, and hits more advanced in (pre)clinical studies, are highlighted. Nocathiacins I–III (91–93), unnarmicins A (114) and C (115), sclerotides A (160) and B (161), and plitidepsin (174) can be highlighted considering not only their high antimicrobial potency in vitro, but also for their promising in vivo results. Marine cyclic peptides are also interesting models for molecular modifications and/or total synthesis to obtain more potent compounds, with improved properties and in higher quantity. Solid-phase Fmoc- and Boc-protection chemistry is the major synthetic strategy to obtain marine cyclic peptides with antimicrobial properties, and key examples are presented guiding microbiologist and medicinal chemists to the discovery of new antimicrobial drug candidates from marine sources.

Desymmetrisation of meso-2,4-Dimethyl-8-Oxabicyclo[3.2.1]-Oct-6-Ene-3-Ol and its Application in Natural Product Syntheses

The compounds containing chiral centers and different functional groups serve as magnificent building blocks for the preparation of various natural products that are having immense biological activity. "Dimethyl-8-oxa-bicyclo[3.2.1]oct-6-en-3-ol" is one of the wonderful synthons to construct multiple stereo centers at a time during the asymmetric synthesis. In this account, we discuss our research efforts toward the synthesis of various simple and complex natural products from the past three decades (1995-2020) by using dimethyl-8-oxa-bicyclo[3.2.1]oct-6-en-3-ol as a synthon. Moreover, the synthetic utility of this starting material was investigated and well demonstrated. Further, we executed the desymmetrization of dimethyl-8-oxa-bicyclo[3.2.1]oct-6-en-3-ol by hydroboration to get different chiral centers. After obtaining the stereocenters, we could manage either the fragment, formal or total synthesis of natural products, by simple protection and deprotection sequence followed by C-C bond formation steps.

Applications of oxazolidinones as chiral auxiliaries in the asymmetric alkylation reaction applied to total synthesis

In this review, a number of applications of chiral oxazolidinones in the asymmetric alkylation reaction applied to total synthesis are described.

Jahanyne, an apoptosis-inducing lipopeptide from the marine cyanobacterium Lyngbya sp

An acetylene-containing lipopeptide, jahanyne, was isolated from the marine cyanobacterium Lyngbya sp. Its gross structure was established by spectroscopic analyses, and the absolute configuration was clarified based on a combination of chiral HPLC analyses, spectroscopic analyses, and derivatization reactions. Jahanyne significantly inhibited the growth of human cancer cells and induced apoptosis in HeLa cells.

A catalytic reactor for the organocatalyzed enantioselective continuous flow alkylation of aldehydes

The use of immobilized metal-free catalysts offers the unique possibility to develop sustainable processes in flow mode. The challenging intermolecular organocatalyzed enantioselective alkylation of aldehydes was performed for the first time under continuous flow conditions. By using a packed-bed reactor filled with readily available supported enantiopure imidazolidinone, different aldehydes were treated with three distinct cationic electrophiles. In the organocatalyzed α-alkylation of aldehydes with 1,3-benzodithiolylium tetrafluoroborate, excellent enantioselectivities, in some cases even better than those obtained in the flask process (up to 95% ee at 25 °C), and high productivity (more than 3800 h(-1) ) were obtained, which thus shows that a catalytic reactor may continuously produce enantiomerically enriched compounds. Treatment of the alkylated products with Raney-nickel furnished enantiomerically enriched α-methyl derivatives, key intermediates for active pharmaceutical ingredients and natural products.

Total synthesis and biological evaluation of grassypeptolide A

Herein, we describe in full our investigations into the synthesis of grassypeptolide A (1) in 17 linear steps with an overall yield of 11.3 %. In particular, this work features the late-stage introduction of sensitive bis(thiazoline) heterocycles and 31-membered macrocyclization conducted at the sterically congested secondary amide site in superb conversion (72 % yield). Biological evaluation indicated that grassypeptolide A significantly inhibited cancer cell proliferation in a dose-dependent manner. It induced cancer cell apoptosis, which was associated with increased cleavage of poly(ADP-ribose) polymerase (PARP) and decreased expression of bcl-2 and bcl-xL. Furthermore, grassypeptolide A also caused cell cycle redistribution by increasing cells in the G1 phase and decreasing cells in the S and G2 phases. In addition, cell cycle arrest was correlated with downregulation of cyclin D and upregulation of p27 and p21.

Total synthesis of padanamides A and B

The first total syntheses of padanamides A and B have been achieved, unambiguously confirming their structures.

Total synthesis and stereochemical revision of lagunamide A

A revised configurational assignment for the marine metabolite lagunamide A is proposed and validated by total synthesis.

Total synthesis of hoiamide C

Hoiamide C was synthesized in 16 steps with an overall yield of 1.8% starting from homoallylic alcohol 18, unambiguously confirming its structure.

Antibacterials from the sea

The ocean contains a host of macroscopic life in a great microbial soup. Unlike the terrestrial environment, an aqueous environment provides perpetual propinquity and blurs spatial distinctions. Marine organisms are under a persistent threat of infection by resident pathogenic microbes including bacteria, and in response they have engineered complex organic compounds with antibacterial activity from a diverse set of biological precursors. The diluting effect of the ocean drives the construction of potent molecules that are stable to harsh salty conditions. Members of each class of metabolite-ribosomal and non-ribosomal peptides, alkaloids, polyketides, and terpenes-have been shown to exhibit antibacterial activity. The sophistication and diversity of these metabolites points to the ingenuity and flexibility of biosynthetic processes in Nature. Compared with their terrestrial counterparts, antibacterial marine natural products have received much less attention. Thus, a concerted effort to discover new antibacterials from marine sources has the potential to contribute significantly to the treatment of the ever increasing drug-resistant infectious diseases.

Total synthesis and stereochemical reassignment of bisebromoamide

A revised configurational assignment for the thiazoline moiety of the marine peptide bisebromoamide is proposed and validated by total synthesis.

Total synthesis of grassypeptolide

The first total synthesis of grassypeptolide, an anticancer cyclodepsipeptide isolated from marine cyanobacteria, has been achieved in 17 steps and an overall 11.3% yield.

Synthesis of the C9-C23 (C9'-C23') fragment of the dimeric natural product rhizopodin

A stereoselective assembly of the C9-C23 (C9'-C23') fragment of rhizopodin, a 38-membered bis-lactone natural product, has been developed. A highly efficient approach to this fragment assembles >50% of the carbon skeleton and the stereochemical elements present in the natural product.